This application claims the priority of German patent document 101 01 666.2, filed Jan. 16, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an array antenna system having an electrically large array antenna.
Array antenna systems are known which have an electrically large array antenna comprising a first antenna subarray and a second antenna subarray. A combination transmission line network is provided, which has an input for receiving an antenna power signal as well as a first output connected to emit a first output signal to the first antenna subarray, and a second output connected to emit a second output signal to the second antenna subarray.
Such array antenna systems according to the prior art typically have antenna subarrays which are arranged side-by-side in the form of antenna halves in a plane. In-phase output signals are supplied to the two antenna halves by the outputs of the combination line network (formed by a power splitter) to generate a sum pattern of the antennas, or oppositely phased output signals are supplied to generate a difference pattern.
Electrically large array antennas, particularly those with standing waves on the feeder lines (resonance feeding system) or those with narrowband radiation elements (such as patch antennas) frequently have very narrow matching widths, with resonance-type dependence of the reflection factor as illustrated in FIG. 3.
Frequently, it is impossible to increase the matching bandwidth of such antennas, or it is possible only at considerable additional expenditures, for example, by means of complex feeding systems. Nevertheless, large bandwidths with a constantly low reflection factor are frequently demanded for example, to permit the operation of frequency division multiplex filters or a constant power yield of transmitter amplifiers without a circulator.
European Patent Documents EP 0 310 661 B1 and EP 0 615 659 B1 disclose array antenna systems which contain a number of spatially mutually separated radiation elements, to which signals are fed which are displaced with respect to one another by a given phase for generating a spatial deflection of the antenna beam.
One object of the invention is to provide an array antenna system of the above-mentioned type which, with respect to the bandwidth, has a low input reflection factor and thus a greater matching bandwidth.
This and other objects and advantages are achieved by the array antenna system according to the invention, which has an electrically large array antenna including a first antenna subarray and a second antenna subarray, and a combination transmission line network having an input for receiving an antenna power signal. A first output of the combination line network is connected to emit a first output signal to the first antenna subarray, and a second output is connected to emit a second output signal to the second antenna subarray. According to the invention, the combination line network contains a phase shifting device for generating a phase displacement between the output signals of the first output and of the second output before they are fed to the antenna subarrays; and features are provided to compensate the phase displacement in the course of the beam of the antenna radiation emitted by the antenna subarrays. The array antenna system according to the invention has a matching bandwidth which is significantly larger than a corresponding conventional array antenna system.
The array antenna preferably comprises two equally large antenna subarrays or it consists of several such pairs of equally large antenna subarrays.
In particular, the first antenna subarray forms a first half-antenna of the array antenna, and the second antenna subarray forms a second half-antenna of the array antenna.
According to a first preferred embodiment of the invention, the phase shifting device generates a phase displacement of 90xc2x0.
Preferably, the devices for compensating the phase displacement cause a displacement between the radiation emitted by the first and second antenna subarrays in the main beam direction, by one quarter of a wavelength in the sense of a compensation of the 90xc2x0 phase displacement generated by the phase shifting device.
According to an aspect of the invention, the antenna subarrays are mutually displaced with respect to the main beam direction of the antenna.
In a preferred embodiment, the antenna subarrays are arranged perpendicular to the main beam direction of the antenna, and are mutually displaced by a quarter of a wavelength.
According to an alternative embodiment, the antenna subarrays are arranged diagonally to the main beam direction of the antenna, and the centers of the antenna subarrays are mutually displaced with respect to the main beam direction by a quarter of a wavelength.
According to a further development of the last-mentioned embodiment, the antenna subarrays are arranged in a common plane.
According to another aspect of the invention, the antenna subarrays are covered by dielectric layers of different dielectric constants which compensate the phase displacement of the radiation emitted by the antenna subarrays.
According to the preferred embodiment, the dielectric layers have such a thickness that they cause a displacement between the radiation emitted by the antenna subarrays by one quarter of a wavelength in the sense of a compensation of the 90xc2x0 phase displacement generated by the phase shifting device.
According to a preferred embodiment, the antenna subarrays are arranged in a common plane.
According to another advantageous embodiment, a first dielectric layer is air, and that a second dielectric layer is a layered medium with a dielectric constant which is greater than the dielectric constant of air.
According to yet another aspect of the invention, waveguide paths with different cross-sectional dimensions are arranged on the antenna subarrays, with cross-sectional dimensions arranged in such a way as to compensate the radiation emitted by the antenna subarrays.
The waveguide paths preferably have a length which differs by a defined amount, so that a displacement is caused of the radiation emitted by the antenna subarrays by one quarter of a wavelength in the sense of a compensation of the 90xc2x0 phase displacement generated by the phase shifting device.
According to another preferred embodiment, the antenna subarrays are arranged in a common plane.
In an advantageous further development, transition paths having a transition from a narrow cross-section to a wide cross-section are provided at the output of the waveguide paths.
Advantageously, the antenna subarrays are electrically large in the direction of the division.
According to still another embodiment of the invention, the antenna subarrays are small in the direction perpendicular to the division.
The reflection factors of the antenna subarrays are preferably identical.
According to still another preferred embodiment of the array antenna system according to the invention, the combination line network has a 4-port power splitter, which is preferably formed by a Wilkinson splitter, a 3-dB directional coupler or an E-H waveguide double-T junction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.